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Mil-13924 class 2 vs class 4

Q. I have a requirement for Black Oxide per MIL-DTL-13924 [on DLA] Class 2 on a 304, 316, welded assembly subjected to intermittent high heat approaching 900 °F. My suppliers don't do class 2 and suggest class 4. I know the EPA difference, but I cannot discern the functional difference from the spec. Can someone help? Thanks

Bob West
QA rep - Phoenix, Arizona
February 21, 2017

A. Hi Bob. It seems from a quick read that the biggest difference is that Class 4 requires the parts to pass a 96-hour salt spray test without any supplemental treatment -- which your shops apparently aren't worried about passing.

I think you'll find paragraph 6.3.2 helpful to your understanding. Although it's problematical for anyone to interpret a spec as it pertains to your parts, when they really don't know much about your parts, Class 4 sounds quite reasonable to me for your type 304 & 316 parts. Good luck.

Regards,

Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
February 2017

Thanks Ted. I've read it several times and just couldn't grasp a functional difference. I appreciate the help!

Bob West [returning]
- Phoenix, Arizona USA
February 21, 2017

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